Degaussing device for color picture tube having parallel-slitted beam-selecting grid

ABSTRACT

A degaussing structure for a video tube which serves to demagnetize the tube and an apertured beam-selecting member in the tube. A shroud surrounds the forward portion of the tube and the apertured beam-selecting member. A pair of degaussing coils which are connected in series are wrapped around cutout areas in the shroud at the top and bottom thereof such that the magnetic flux produced by the current carrying coils is in a direction to degauss the apertured beam-selecting member.

United States Patent 1 13,571,652

[72] Inventors Kenjiro Shiobara; [56] References Cited Yuzo Fuse. T kyJapan UNITED STATES PATENTS [211 P 815,940 3,317,781 5/1967 Barbin etal. 315/8 [221 PM 1969 3 324 344 6/1967 Norle 315/8 [451 Patented 1971 3340 417 9/1967 Panis li'gi 315/8 [73] Assignee Sony Corporation Tokyo,Japan Primary Examiner-John Kominski [32] Priority Apr. 14, 1969Assistant ExaminerV. Lafranchi [33] Japan Attorneys-Albert C. Johnston,Robert E. Isner, Lewis H. [3 l 43/24594 Eslinger and Alvin Sinderbrand[54] ABSTRACT: A degaussing structure for a video tube which dema netizethe tube and an a ertured beam-select- SELECTING GRID g p mg member mthe tube. A shroud surrounds the forward por- 3 Chums 7 Drawmg tion ofthe tube and the apertured beam-selecting member. A [52] U.S.Cfl 315/8,pair of degaussing coils which are connected in series are 317/1575wrapped around cutout areas in the shroud at the top and bot- [51] Int.Ci HOlj 29/06 tom thereof such that the magnetic flux produced by thecur- [50] Field of Search 315/8; rent carrying coils is in a directionto degauss the apertured 317/1575 beam-selecting member.

PATENTED HAR23I97I 3,571,652

v INVENTORS KENJIRO SHIOBARA YUZO FUSE av 1 Ail J-L IQyW ATTORNEYDEGAIJSSWG DEVICE FOR COLGR PICTURE TUBE HAVillGFAiikAisiLlEL-SLETTEDBEAM-SELEC'I'ENG GRID This invention relatesgenerally to video tubes of television receivers, and more particularlyis directed to degaussing devices for such tubes.

The deleterious effects of the earths magnetism and the influence ofmagnetic fields from motors such as found in appliances on the videotubes of television receivers are well known. Various devices have beensuggested in the prior art to overcome the ill effects of stray magneticfields; the most notable of these devices being a coil surrounding thevideo tube. The prior art devices did not effectively remove the effectsof stray magnetic fields, however, and they required a relatively largeamount of power.

The present invention seeks to improve on the prior art degassingdevices in a simple, efficient and inexpensive manner. A relativelylarge magnetic shroud which has a high permeability such as sheet steelis attached to and surrounds the envelope of the video tube at theforward end adjacent the screen. A pair of coils having AC currentpassed therethrough and being magnetically coupled to the shield areselectively mounted on the video tube. A grid such as an aperture grillor a shadow mask for attracting electrons is also included in themagnetic flux path whereby the screen and the grid in the video tube aredegaussed in a highly efficient manner.

The above, and other objects, features and advantages of the inventionwill be apparent in the following detailed description of illustrativeembodiments thereof which is to be read in connection with theaccompanying drawings, wherein:

FIG. 1 is a side view partly in section showing a degaussing devicemounted on a video tube;

FIG. 2 is a top view showing the structure of the degaussing shield anda portion of the coil;

FIG. 3 is a side view partly in section showing another embodiment ofthe invention;

FiG. i is a top view showing details of the FIG. 3 embodiment;

FIG. 5 is a view taken along the line 5-5 of FIG. 2;

FIG. 6 is a view taken along the line 6-6 of FIG. 1; and

FIG. 7 is a circuit diagram showing a degaussing circuit.

Referring to PEG. 1, there is shown a video tube 10 which is commonlyused in television receivers. The video tube 10 comprises a screen 12which is provided on the faceplate of a glass envelope further having afunnel-shaped section 13 and a neck 14 extending therefrom.

A beam deflection yoke 15, which is well known in the art, iscircumferentially mounted on the neck M of the video tube. Since thebeam deflection yoke 15 forms no part of this invention, further detailis not required concerning its operation.

A shroud to which is formed of a material having a high permeance suchas annealed sheet steel surrounding it and is closely maintained on theexterior surface of the video tube 10 such that a portion 16a isdesigned to follow the contour of the funnel-shaped portion E3 on thetube envelope. A front portion lob fits snugly against the flat portionof the video tube just behind the screen 112. The shroud 16 is formedwith a raised portion rec rearwardly of the front portion or flange Ebb,and laterally spaced slots 119a and 1% (FIG. 2) are formed in raisedportion 160 and flange 16b at the opposite sides of the top and bottomof shroud 1b, with such slots opening at the free edge of flange 16b. Acoil llla is wound on the top portion of shroud 16 between the slots 19aand 19b and coil 1 lb is similarly wound on the bottom portion of shroudIn between the slots Na and 19b in such bottom portion. The coils Illaand lib are connected in series and have an AC current passedtherethrough, for example, as hereinafter described in detail.

An apertured beam-selecting member 17 which is preferably a grid havinglongitudinal slits 17a therein and having high permeance is arranged inproximity with the shroud portion H612 to enable the flux path from thecoils Illa and Nb to pass through the grid. The details of theaforementioned grid or aperture grill are more fully disclosed incopending ap plication Ser. No. 790,350 filed .Ian. 10, I969, andentitled Grid Structure For Color Picture Tubes" assigned to the sameassignee as this application. A frame 18 which can be of any knownconstruction and preferably of high permeance is mounted within thevideo tube in any known manner such that it supports the grid 17 in anupright position. When an aperture grill is used in which elongatedslits are formed in a grid, the coils are located adjacent the upper andlower portions respectively of the slits in the aperture grill such thatthe flux path emanating from the coils is parallel to the longitudinalaxis of the substantially parallel slits in the aperture grill. With thelatter arrangement demagnetization of the aperture grill can be properlyeffected. Since the flux path does not extend around the peripheralportion of the tube between the coils, the reluctance of the magneticcircuit is greatly reduced, thereby decreasing the power losses whichnecessarily result from a longer flux path.

It will be seen that a magnetic loop is formed by the front portion orflange 16b of shroud to, the frame 118 and the grid 17, and by theportion I611 of the shroud. This magnetic loop is formed to degauss thevideo tube and the grid by current flowing through the degaussing coilsllaand lib such that the grid 17 and the frame I8 are demagnetized bythe degaussing field. The reluctance of the magnetic conductive loopincluding the grid I7 is so small that demagnetizing is accomplishedwith low power loss and high efficiency.

In the embodiment of the invention shown in FIGS. 3 and 4, a peripheralring 26 surrounds the front of the tube. The ring is also formed of amaterial having a substantially high permeance such as sheet metal. Thering 26 protects the tube from explosion since it serves to reinforcethe latter. The magnetic conductive loop is formed as in the previousembodiment, however, the flux now passes through the ring 26. The ringhas a flange 26a thereon which abuts a corresponding flange ltid on theshroud to. Because of the added ring 26 and the additional degaussingeffect therefrom, a highly effective and efficient demagnetizingoperation is effectuated. The coils Ma and lib are arranged as in theprevious embodiment.

In FIG. 7 there is shown a degaussing circuit which includes a powertransformer 20), a thermistor 2i and a varistor 22 in paralleltherewith. The degaussing coils Ma and lib are connected in series. Abridge rectifier 23 changes that AC input to pulsating DC and acondenser 24 removes the pulsations and completes the circuit to DCoutput terminals 25 which may constitute a source of DC for any desiredcircuit in the receiver. The circuit depicted in FIG. 7 is an automaticdegaussing circuit. The coils Ma and Ilb are energized through thevaristor 22 while the television receiver is warming up. As the setwarms up the resistance of the varistor increases until it blocks thecurrent flowing through the coil 11, but the current through thethermistor 2i continues.

For the purpose of illustrating the present invention, a specific typeof electron beam selection means has been disclosed. It should beunderstood, however, that the aspects of the present invention areapplicable to various types of electron beam selection devices wellknown to those those skilled in the art as well as others and it is notintended to limit the present invention to the specific type disclosedand illustrated herein.

We claim:

IL. The combination of a color video picture tube comprising a tubeenvelope having a face plate at one end with a phosphor screen thereon,an apertured beam-selecting means mounted within said envelope adjacentsaid screen and having the apertures thereof in the form of parallel,elongated slits, a shroud of substantially high permeance partiallycovering the tube envelope and having a portion thereof adjacent saidbeamselecting means, degaussing coils carried by said shroud at opposedlocations on the latter such that a degaussing current passed throughsaid coils produces a magnetic flux which passes through said tubeenvelope and through said beamselecting means in the direction of saidparallel slits prior to return to said coils by way of said shroud, andcircuit means wrapped about the top and bottom sections of said raisedportion between the respective cutouts therein.

3. The combination according to claim 2, in which said edge portion isconstituted by a radial flange. and a ring of high permeance extendsaround the tube envelope in the region of the face plate and has aradial flange abutting said flange constituting said edge portion toprovide with the latter a path for the magnetic flux.

1. The combination of a color video picture tube comprising a tubeenvelope having a face plate at one end with a phosphor screen thereon,an apertured beam-selecting means mounted within said envelope adjacentsaid screen and having the apertures thereof in the form of parallel,elongated slits, a shroud of substantially high permeance partiallycovering the tube envelope and having a portion thereof adjacent saidbeam-selecting means, degaussing coils carried by said shroud at opposedlocations on the latter such that a degaussing current passed throughsaid coils produces a magnetic flux which passes through said tubeenvelope and through said beam-selecting means in the direction of saidparallel slits prior to return to said coils by way of said shroud, andcircuit means for supplying said degaussing current to said coils in theform of a progressively decreasing AC current during warmup of the colorvideo picture tube.
 2. The combination according to claim 1, in whichsaid slits extend vertically, said portion of the shroud adjacent thebeam-selecting means is an edge portion thereof and an adjacent raisedportion, said shroud has cutouts extending from said edge portion intothe adjacent raised portion at opposite sides of the top and bottom ofthe shroud, and said coils are wrapped about the top and bottom sectionsof said raised portion between the respective cutouts therein.
 3. Thecombination according to claim 2, in which said edge portion isconstituted by a radial flange, and a ring of high permeance extendsaround the tube envelope in the region of the face plate and has aradial flange abutting said flange constituting said edge portion toprovide with the latter a path for the magnetic flux.